DOS 4.1 is a reimagined Disk Operating System for the Apple II computer, released in 2018. Programmed by Walland Philip Vrbancic, Jr., a professional programmer since 1983. It contains the power and the flexibility that he always thought DOS should have, while remaining compatible with DOS 3.3. This book, encompassing over 240 pages, explains all new features in detail. Highlights of DOS 4.1 Improvements: - A rebuilt Zero Page, faster Variable Handling, more extensive Time Stamps, and an Expanded Catalog and File Manager. - Complete support for Language Cards and popular Clock cards, as well as additions for homebrew ROM modifications. - Included tools have been enhanced specifically for DOS 4.1, including Big Mac, CFFA Volume Manager, Disk Window, GPLE, Sourceror, and others. - Many new commands and enhancements to existing commands.